Uplink power control using power spectral density to avoid adjacent satellite interference

ABSTRACT

A method and apparatus for uplink power control based on power spectral density are disclosed. In one embodiment, the method for use by a terminal in a satellite communication system, the terminal having an antenna, a modem and a controller, the method comprising: determining the scan and skew of the antenna; obtaining, using the controller, a value representing a maximum allowed Power Spectral Density (PSD) for the determined scan and skew; determining, using the controller, a maximum allowable modem power based on the value representing a maximum allowed PSD, where the maximum allowable modem power is that which ensures that transmissions from the terminal do not exceed the maximum allowed PSD if the maximum allowable modem output power is not exceeded by the modem; sending, using the controller, an indication of the allowable modem output power to the modem; and performing one or more transmissions from the terminal based on modem outputs in accordance with the maximum allowable modem output power.

PRIORITY

The present patent application claims priority to and incorporates byreference corresponding provisional patent application No. 62/786,795,titled “Method for Determining Maximum Power Spectral Density to AvoidAdjacent Satellite Interference,” filed on Dec. 31, 2018; andprovisional patent application No. 62,924,519, titled “Method forDetermining Maximum Power Spectral Density to Avoid Adjacent SatelliteInterference,” filed Oct. 22, 2019.

FIELD OF THE INVENTION

Embodiments of the present invention relate to wireless communication;more particularly, embodiments of the present invention relate to uplinkpower control for satellite antennas that is based on power spectraldensity.

BACKGROUND

In the world of GEO satellite communications, the equatorial plane some36,000 km away from the surface of the earth is typically populatedevery 2 degrees in longitude with a satellite. The satellite industryshares the frequency spectrum. This places a burden on the satellitecommunications user segment (antennas) to produce pencil-beam emissions.These pencil beams focus as much of its energy as possible on its targetsatellite, while protecting neighboring satellites from unwanted and/orharmful interference through spatial isolation.

It would be difficult to design an antenna that radiates zero energytowards neighboring satellites. This is widely recognized in thesatellite industry, and some energy is expected to radiate towardsunwanted satellite(s). However, it is critical to control the energylevels in these instances below acceptable thresholds. Satelliteoperators in coordination with ITU, FCC and other regulatory bodies haveproduced rules for maximum permissible power levels as a function ofoff-axis angles (away from target satellite). These rules are known asPower Spectral Density (PSD) masks, and they slightly vary depending ongeographical region and satellite orbit slot nature. As such, mostcommonly enforced PSD masks are:

FCC PSD Mask

ITU PSD Mask

Coordinated PSD Mask

To stay compliant with regulatory PSD masks, an antenna/terminaloperator has two choices: expand bandwidth of the channel in use whennon-compliance is detected or lower the power output of the terminalwhen non-compliance is detected. In certain commercial satellitecommunication network configurations, bandwidth of the transmit (Tx)channels is fixed and cannot be changed dynamically, leaving powerback-off as the only option.

SUMMARY OF THE INVENTION

A method and apparatus for uplink power control based on power spectraldensity are disclosed. In one embodiment, the method for use by aterminal in a satellite communication system, the terminal having anantenna, a modem and a controller, the method comprising: determiningthe scan and skew of the antenna; obtaining, using the controller, avalue representing a maximum allowed Power Spectral Density (PSD) forthe determined scan and skew; determining, using the controller, amaximum allowable modem power based on the value representing a maximumallowed PSD, where the maximum allowable modem power is that whichensures that transmissions from the terminal do not exceed the maximumallowed PSD if the maximum allowable modem output power is not exceededby the modem; sending, using the controller, an indication of theallowable modem output power to the modem; and performing one or moretransmissions from the terminal based on modem outputs in accordancewith the maximum allowable modem output power.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given below and from the accompanying drawings of variousembodiments of the invention, which, however, should not be taken tolimit the invention to the specific embodiments, but are for explanationand understanding only.

FIG. 1 illustrates concepts of both scan and skew assuming ahorizontally mounted antenna subsystem module (ASM).

FIGS. 2-5 illustrate different radiation patterns measured along thegeostationary arc axis.

FIG. 6 illustrates an example of a closed-loop uplink power control(UPC) process.

FIG. 7 is an example of the effective width and height as a function ofelevation angle for one embodiment of an ASM.

FIG. 8 illustrates multiple different beams and a representative amountof their beam spreading as theta increases.

FIG. 9 illustrates skew angle as a function of terminal location onEarth.

FIG. 10 illustrates power transfer curve relating block upconverter(BUC) output power to modem power out.

FIG. 11 is a flow diagram of one embodiment of a process for controllinga satellite antenna in a satellite communication system.

FIG. 12 is a block diagram of a terminal that performs the process ofFIG. 11.

FIG. 13 is a flow diagram of one embodiment of a process for determiningthe allowable modem power.

FIG. 14 illustrates a data flow diagram depicting one embodiment of aUPC process.

FIG. 15 is a flow diagram of one embodiment of a process for controllingan antenna.

FIG. 16 is a flow diagram of one embodiment of another uplink powercontrol process.

FIG. 17 is a sequence diagram of one embodiment of a UPC processinvolving a modem and hub in a satellite communication system.

FIG. 18 illustrates an example of PSD limits for different regions.

FIG. 19 is a flow diagram of one embodiment of a UPC process thatperforms a mute operation to mute the terminal based on theta, skew, andbandwidth.

FIG. 20 is a flow diagram of one embodiment of a UPC process thatperforms modem power control based on theta, skew, and bandwidth.

FIG. 21 is a flow diagram of one embodiment of a UPC process thatcontrols a mute operation based on PSD thresholds.

FIG. 22 is a flow diagram of a UPC process that uses worst-case values.

FIG. 23 is a flow diagram of a UPC process that uses database of PSDmaximum values.

FIG. 24 is a flow diagram of a UPC process that is optimized using dataanalysis.

FIG. 25 illustrates the schematic of one embodiment of a cylindricallyfed holographic radial aperture antenna.

FIG. 26 illustrates a perspective view of one row of antenna elementsthat includes a ground plane and a reconfigurable resonator layer.

FIG. 27 illustrates one embodiment of a tunable resonator/slot.

FIG. 28 illustrates a cross section view of one embodiment of a physicalantenna aperture.

FIG. 29A-D illustrate one embodiment of the different layers forcreating the slotted array.

FIG. 30 illustrates a side view of one embodiment of a cylindrically fedantenna structure.

FIG. 31 illustrates another embodiment of the antenna system with anoutgoing wave.

FIG. 32 illustrates one embodiment of the placement of matrix drivecircuitry with respect to antenna elements.

FIG. 33 illustrates one embodiment of a TFT package.

FIG. 34 is a block diagram of one embodiment of a communication systemhaving simultaneous transmit and receive paths.

DETAILED DESCRIPTION

In the following description, numerous details are set forth to providea more thorough explanation of the present invention. It will beapparent, however, to one skilled in the art, that the present inventionmay be practiced without these specific details. In other instances,well-known structures and devices are shown in block diagram form,rather than in detail, in order to avoid obscuring the presentinvention.

Overview of Uplink Power Control

Embodiments of the invention include techniques for controlling theuplink power for a terminal's antenna in a satellite communicationsystem. In one embodiment, controlling the uplink power of a terminal'santenna impacts the user's “upload” data rate. In one embodiment, onegoal is to be as close to the PSD limit as possible while holding enoughmargin to be confident that the PSD will not exceed pre-calculatedlimits, and the closer the PSD is to the limit, more modulation andcoding schemes may be used which allow for a larger data rate to beachieved. Techniques described herein enable a very dynamic Uplink PowerControl (UPC) to keep up with fast changing sidelobe content in adynamic tracking environment.

In one embodiment, the UPC is performed using the Power Spectral Density(PSD) limit. The PSD of an antenna is defined as the EquivalentIsotropic Radiated Power (EIRP) divided by the ratio of bandwidth of thetransmitted signal versus a designated bandwidth per the regulatorybody. Different space regulations (e.g., FCC, ITU, etc.) have differentstandards and maximum allowances for PSD. For example, the FCC, whichregulates the space and frequency over the United States, has a densityrequirement of dBW/4 kHz bandwidth, whereas the ITU has a densityrequirement in units of dBW/40 khz and governs most of the rest of theworld. Therefore, for different locations on the Earth, in oneembodiment, the terminal is aware of the region in which it is located,and with that, what requirements it must follow. It is also not uncommonfor a satellite operator to set its own PSD limits for a satellite thatmay be more strict than the limit set by the ruling space regulationcommittee.

In one embodiment, the satellite antenna is a flat-panel antenna thatelectronically steers a beam using antenna elements. Examples of such anantenna are described in more detail below. In one embodiment, theantenna updates its beam shape at predetermined intervals (e.g., every 4msec). This causes its radiation pattern to update. Every time such anupdate to the radiation pattern occurs, the sidelobes and maximumallowed PSD may change. In one embodiment, the UPC is performed toensure that the maximum allowed PSD is not exceeded.

A simple method to perform UPC using PSD is to find the worst-caseradiation pattern and sidelobes for a beam from a transmitting antenna,and then set that as the maximum PSD for all theta/scan conditions. Inone embodiment of the antenna, this smallest maximum PSD occurs at anextreme case of high scan and skew angles. Therefore, if the worst-casePSD were applied to all scenarios, connectivity would not be possibledue to the PSD limit being below what is required by the modem totransmit data.

To conform to the regulations of both the FCC and ITU while also beingable to transmit data, in one embodiment, PSD maximum value tables aregenerated in 5-degree steps where all radiation patterns within theconstraints of the specific cell are analyzed and a maximum PSD isevaluated to ensure compliance for all operation conditions. In oneembodiment, there are four tables, two for the FCC and two more for ITUregulations. In one embodiment, the antenna (e.g., ASM) performsdifferently depending on whether it is transmitting in horizontal orvertical polarization, and the radiation patterns are different enoughwhere separating the two polarizations into two different sets ofrequirements allows for a higher EIRP transmission. Tables 1A and 1Bbelow is an example of one of the FCC tables.

TABLE 1A SKEW SCAN 0 5 10 15 20 25 30 35 40 0 15.22 15.72 15.72 14.7113.45 13.2 13.69 13.94 12.93 5 15.81 15.31 15.06 15.06 14.56 14.06 14.3114.81 14.81 10 15.44 15.44 15.44 15.19 14.94 15.19 16.19 15.44 16.44 1515.46 15.21 15.21 15.21 15.46 15.46 15.96 15.96 16.21 20 15.26 15.0115.01 14.76 14.26 14.26 15.01 15.51 15.76 25 15.45 15.2 14.95 14.7 14.213.95 14.45 15.45 15.45 30 15.64 15.89 15.64 15.39 14.64 14.39 14.8913.64 15.39 35 16.15 16.15 15.65 13.9 12.65 11.9 11.65 11.9 10.48 4015.23 15.48 15.23 13.98 11.73 10.48 9.73 9.73 10.48 45 12.91 13.91 15.6615.16 12.91 11.41 10.41 10.16 10.91 50 14.49 15.24 14.99 .14.49 13.9912.49 11.49 10.99 10.99 55 15.52 15.27 14.77 14.27 12.52 11.02 10.029.52 9.27 60 15.41 15.66 15.16 14.66 13.91 12.16 10.41 9.16 8.41 6515.53 15.28 15.03 14.53 13.03 11.28 9.78 8.28 .7.03 70 14.59 14.84 14.5913.09 11.34 10.09 8.59 7.34 6.09 75 11.38 11.38 11.13 10.63 10.88 9.638.13 6.88 5.63

TABLE 1B 45 SCAN 50 55 60 65 70 75 80 85 90 0 15.42 14.91 14.9 15.8916.38 16.88 15.88 14.88 14.13 5 16.06 14.81 15.81 15.56 14.81 14.0613.56 13.31 13.06 10 16.44 15.19 14.94 14.94 14.44 13.69 13.44 12.9412.94 15 16.21 15.21 15.46 14.96 14.21 13.71 13.21 12.96 12.96 20 16.2616.01 14.76 14.26 14.26 13.76 13.26 13.01 13.01 25 15.45 13.95 13.212.45 12.45 12.95 12.95 12.7 12.7 30 15.39 14.14 12.64 11.89 11.89 12.3912.39 12.39 12.64 35 14.65 14.4 13.15 11.65 11.4 11.65 12.65 12.4 12.440 13.48 13.23 10.98 9.98 10.48 11.98 11.73 11.48 11.23 45 13.91 13.1610.66 8.91 8.16 8.66 10.41 10.91 10.66 50 12.49 12.49 11.24 8.74 6.996.74 8.24 9.99 9.74 55 11.27 11.27 10.02 7.02 5.52 5.52 7.02 8.52 8.2760 8.16 9.91 10.16 8.16 4.91 4.91 4.91 6.91 6.91 65 6.28 6.78 8.28 7.035.28 4.03 4.03 6.03 5.78 70 3.84 3.09 3.34 5.59 6.09 5.34 4.09 3.84 4.3475 3.38 2.88 3.63 5.38 4.63 3.88 3.38 3.63 2.88

In one embodiment, each cell in tables 1A and 1B are the maximum PSDallowed for that theta/scan condition. The maximum PSD would be thevalue where the antenna's current skew and theta intersect (e.g. skew 20degrees, theta 45 degrees would be a PSD of 12.91 dBW/4 kHz). In oneembodiment, this value is used to control the modem to ensure that thecombination of bandwidth and transmit power is below the specified PSDlimit. As the antenna moves, the scan and skew will update to newvalues, where the PSD value may change. In one embodiment, if there isenough change where either the scan or skew value moves to a differentcell in tables 1A and 1B, the new maximum PSD is used to control themodem so that the modem controls its power to ensure that thecombination of bandwidth and transmit power is below the specified PSDlimit once the signal is transmitted from the antenna. In oneembodiment, obtaining new PSD maximum values for controlling the modemis dynamic and nearly instantaneous.

FIG. 1 illustrates concepts of both scan and skew. Referring to FIG. 1,scan is the angle between the vector of the antennas' boresight andbroadside vectors. The electronically steered antenna (ESA) gain andantenna beam width depend on the effective area of the antenna in thedirection of the satellite. As the scan angle increases, the effectivearea decreases which results in both lower gain and a wider beam alongthe axis of the reduced area. Since only the beam will widen on the axisof reduced effective area, the location of the terminal with respect tothe satellite also affects the maximum PSD. This is because as theterminal moves closer to the equator, the axis of reduced effective areabecomes more in line with the geostationary arc, which means that thebeam widening falls along the GEO arc and the widening of the beam willintroduce unwanted noise to adjacent satellites. This angle is skew, andtypically as both scan and skew angles increase, the power is reduced toensure the antenna is not interfering with neighboring satellites (thisis noticeable in the bottom right section of the table above). Skewangle is defined by the terminal's location on Earth relative to thelocation of the satellite in space. Any point on the globe that is onthe same line of longitude as the satellite has a skew angle of zero.Any point along the equator has a skew angle of 90 degrees. FIG. 9illustrates skew angle as a function of terminal location on the Earth.

FIGS. 2-5 illustrate different radiation patterns measured along thegeostationary arc axis. To better illustrate the beam widening, FIG. 2is focused only on the main lobe and first few sidelobes. Note that thefull analysis evaluates from −180 to +180 degrees.

The first image in FIG. 2 is for a scan of 0 degrees (which is definedherein as theta) and a skew of 0 degrees. As the PSD in the top box isdBW/40 kHz, this is evaluating against the ITU specification. This is atypical beam width for one embodiment of an antenna subsystem module(ASM). For purposes herein, in one embodiment, an ASM is a stackup andset of antenna components that includes a radome, TFT substrate, dipole,elements, feed assembly, control electronics and connectors, and abackshell, and the terminal comprises the ASM, a modem, an LNB, and aBUC. As theta increases, and the skew stays at 0 degrees (as shown inFIG. 3), the beam shape does not change along the geostationary arcsince the beam widening is orthogonal to the GEO arc.

However, as skew increases along with scan, the beam widening is alongthe GEO arc and the main lobe and sidelobes begin to widen, pushing theprevious compliant radiation pattern towards the specification PSD maskuntil it exceeds the PSD mask. FIGS. 4 and 5 illustrate different skews.FIG. 4 is an intermediate skew where the PSD mask is not violated, butthe beam widening is noticeable, and FIG. 5 is when the mask is violatedand a PSD back-off is required to stay compliant. The amount of back-offis noted in FIGS. 4 and 5 as “PSD Back-off”. Note that the roll-off tothe right side of FIGS. 4 and 5 is due to those angles being below theface of the antenna where no transmissions are possible.

In one embodiment, the flat panel antenna does not need to pointdirectly to the satellite it is communicating with because it is able toelectronically steer the beam to keep it pointing at the satelliteregardless of terminal location or antenna orientation. Steering thebeam this way creates changes in gain and beam shape as a function ofthe theta angle.

Theta at zero degrees is a beam leaving the face of the antenna at avector that is normal to the antenna surface, increasing to a value of90 degrees which is parallel to the surface of the antenna. As the thetaangle increases, the beam elongates in the direction parallel to avector in a plane the direction the beam is angled. The location of theantenna on the Earth relative to the position of the satellite defines a“skew angle”, which determines the shape of the beam as seen relative tothe GEO arc.

This elongation of the beam can cause part of the energy of theantenna's radiation pattern being transmitted to cause adjacentsatellite interference (ASI). When in this state, the terminal mustreduce power to be below some maximum threshold to avoid ASI andregulatory violations.

In one solution to this problem, some networks provide a closed-loopcontrol for uplink power as part of its UPC. Measurements are made onthe network hub to determine minimum and maximum power spectral density(PSD) which are then sent to the modem, which forwards this informationon to the antenna. The antenna then calculates the current transmittedPSD, and if it falls outside of the limits the terminal is muted. FIG. 6illustrates an example of a closed-loop UPC process. Other networksolutions do not provide this closed loop control, so the terminal doesnot know what the limit of the power spectral density (PSD) value can bewithout muting. In such cases, a very conservative algorithm is usedthat limits PSD to the worst case possible by considering all theta andskew angles. However, there are situations where the terminal's outputpower could be safely increased above the limits found in the PSD tablewithout causing ASI or regulatory violations. Techniques describedherein provide possible ways to achieve this higher performance withoutnetwork closed-loop control.

In one embodiment, the beam shape from the electronically steered flatpanel antenna is based on the effective area of the antenna, which isthe combination of effective height and width that is visible to thesatellite through which the Earth terminal is communicating. FIG. 7 isan example of the effective width and height as a function of theta forone embodiment of an ASM. As the effective area of the ASM decreasesfrom the perspective of the satellite the beam will widen along the axisof the decreased area. As the ASM is tilted, the look angle (theta)increases and the effective area decreases.

FIG. 8 illustrates multiple beam shapes that may be generated from oneembodiment of an electronically steered antenna depending on orientationand theta, such as those described, for example, in more detail below.When the beam is generated when the antenna is broadside (normal to theantenna surface), the beam shape is round. As the theta angle increases,the beam will widen in the direction which the antenna presents lesssurface area. In the case of the antenna of FIG. 7 there is less surfacearea presented vertically (with respect to this page), so the beam wouldelongate in the vertical direction.

In general, if a flat panel antenna is located at a place on Earth withhigh skew and has a beam that is non-circular, the chances of ASIhappening are greater.

Examples of UPC Processes

In one embodiment, UPC may be performed by a user terminal antennaitself. In other words, the UPC process is performed without confirmingpower measurements using the hub, which is generally controlled by anetwork provider separate from the antenna/terminal producer. Becausethe hub is not involved in the UPC process, the monitoring on the hubside and the passing messages back through a link with 1-2 seconds oflatency is avoided as well (i.e., the process is not “laggy”).

In one embodiment, the UPC process derives a maximum modem output powerin real-time. This is done by obtaining a maximum PSD value and usingthat value to determine the maximum modem output power. In oneembodiment, this determination is performed on the antenna by acontroller (e.g., one or more processors). The maximum modem outputpower is signaled to the modem, which limits its output power to belowthe specified maximum, thereby ensuring that the terminal operates in away that does not exceed the PSD limit. Note that because the modemreceives a signal regarding its maximum allowable output power from acontroller on the terminal and controls its output power accordingly(and thus does not have to determine its output power), embodiments ofthis invention are modem/network agnostic and thus can be used by anymodem provider as long as they possess the capabilities to implementthis on their products.

There are a number of key innovations associated with the UPCtechniques. First, in one embodiment, these techniques use the resultsfrom the P1dB curve which is run during terminal commissioning tounderstand a relationship between modem output power and the terminal'sblock upconverter (BUC) output power. By relating the modem output powerto the BUC output power, a maximum modem output power can be calculatedfor the current scan and skew condition of the ASM by correlating amaximum PSD transmitted out of the antenna, to a maximum BUC power (orpower density), which may then be correlated to a modem power (or PSD)by the implementation discussed above in this paragraph. FIG. 10illustrates an example of a power transfer curve relating the BUC outputpower to modem output power.

By increasing the power out of the modem by a set level (e.g., 1 dB) andrecording the response from the BUC, an output power of the modem ismapped to the BUC for the entire power curve of the BUC, such as shownin FIG. 10. In one embodiment, this is important since the saturationpoint of the BUC is known and a particular BUC power to a modem powerrelationship can be determined which will stay consistent as long as Txcables and the set gain within the BUC are not changed. If the BUC gainis changed, the curve may be offset, meaning that UPC would still bepossible, but the offset will need to be considered if/when fullyimplemented. In one embodiment, some margin is held for temperature,unit variation, etc.

Once that curve is known, a reverse calculation is made of the maximumpower required if the modem passes the ASM the symbol rate and/orbandwidth (e.g., transmit power). In one embodiment, these techniquesinclude receiving the current symbol rate from the modem through amessage (e.g., OpenAMIP message, etc.).

As another innovation, in one embodiment, the UPC process includessending a message to a modem that states the maximum allowable modempower to be PSD compliant. That is, the maximum modem output power issent to the modem using a single message. In another embodiment, themodem is sent a power density rather than the maximum modem outputpower. In one embodiment, with the PSD at the output of the ASM and thegain of the ASM, BUC, and cables being known, the ASM translates the TxPSD to modem PSD without needing the symbol rate from the modem, and theASM can transmit a single message to the modem in terms of density. Inresponse to such a message, the modem calculates power based on thesymbol rate (which the modem knows).

The techniques described herein enable a number of improvements,including, but not limited to, being able to remove the power margin fortheta uncertainty based on time delay (because having to go to the hubfor UPC is no longer necessary and the margin associated with this delayis avoided), no longer having to rely on the hub infrastructure, whichallows for sending required messages to and from the antenna subsystemmodule (ASM) via a single connection, and is less complicated and moreaccurate.

The features enable the antenna to no longer need to communicate withthe hub, thereby allowing the response to go from seconds toinstantaneous. Furthermore, using the techniques disclosed hereinenables the loss between the modem and ASM to stay consistent oncecommissioning has occurred.

FIG. 11 is a flow diagram of one embodiment of a process for controllinga satellite antenna in a satellite communication system. In oneembodiment, the process is performed by processing logic that maycomprise hardware (circuitry, dedicated logic, etc.), software (e.g.,software running on a chip), firmware, or a combination of the three. Inone embodiment, operations of the process of FIG. 11 are performed by acontroller, including one or more processors, of the satellite antenna.

Referring to FIG. 11, the process begins by processing logic determiningthe scan and skew of the antenna (processing logic 1101). In oneembodiment, at each beam update interval (e.g., each time the liquidcrystal pattern for the liquid crystal (LC) in the antenna elements isupdated), the scan and skew of the antenna are calculated. Examples ofsuch antenna elements that may be used on antenna apertures that arepart of antenna using one or more power control processes describedherein are described in more detail below. Even so, the techniquesdescribed herein are not limited to such antenna elements.

Next, processing logic obtains a value representing a maximum allowedPSD for the determined scan and skew (processing logic 1102). Themaximum PSD value is that which meets a regulatory limit as describedabove. In one embodiment, this value is obtained by a controller of theantenna. In one embodiment, the controller is part of the ASM. In oneembodiment, the maximum allowed PSD is obtained from a look-up table(e.g., for correct regulatory environment and polarization), such as,for example, those described herein, using the skew and scan values. Inone embodiment, the table is stored in a memory in the terminal (e.g.,in the ASM) and is accessed by the controller.

After the maximum allowed PSD is obtained, processing logic determinesan allowable modem power based on the value representing a maximumallowed PSD (processing logic 1103). In one embodiment, the allowablemodem output power is the maximum allowable modem output power, suchthat the maximum allowed PSD is not exceeded by the antenna if themaximum allowable modem output power is not exceeded by the modem duringtransmissions from the antenna.

In one embodiment, the controller in the ASM determines the allowablemodem power. Since this determination is made by a controller on theantenna, the allowable modem power is determined without communicationwith a hub in the satellite communication system.

Once the allowable modem power has been determined, processing logicsends an indication of the allowable modem output power to the modem tocontrol the modem (processing block 1104). In one embodiment, theindication comprises a value of the actual modem output power. Inanother embodiment, the indication comprises an encoded alpha-numericvalue that the modem uses to determine the allowable modem power. In oneembodiment, the encoded alpha-numeric value is a modem power densityvalue. In one embodiment, the controller sends the indication of theallowable modem output power to the modem by sending a single messagefrom the ASM of the antenna to the modem.

After sending the indication of the maximum modem output power,processing logic causes the terminal to transmit one or moretransmissions based on modem outputs in accordance with the maximumallowable modem output power (processing block 1105). That is, inresponse to the allowable modem output power (e.g., the maximumallowable modem output power), processing logic controls the power thatthe modem outputs to the antenna aperture (e.g., an antenna aperture ofan ASM) to remain at or below the allowable modem output power. That is,the allowable modem power that is set based on the maximum allowed PSDis used to control the modem, which controls the power being transmittedby the antenna. By doing so, the antenna aperture is ensured ofoperating within the regulatory limits (e.g., the PSD limit).

FIG. 12 is a block diagram of a terminal for use in a satellitecommunication system that performs the process of FIG. 11. In oneembodiment, the antenna comprises an electronically-steered flat-panelantenna such as, for example, but not limited to, an antenna describedin further detail below.

Referring to FIG. 12, terminal 1250 includes an ASM 1251 that includesan antenna aperture 1252. In one embodiment, aperture 1252 has radiatingantenna elements operable to radiate radio frequency (RF) signals. Inone embodiment, the antenna elements comprise surface scatteringmetamaterial antenna elements. Examples of such antenna elements aredescribed in more detail below.

Terminal 1250 includes a modem 1254 that is coupled to and providesmodem power 1255 to ASM 1251 for transmission and reception of antennaaperture 1252.

Terminal 1250 also includes a controller 1253 coupled to modem 1254. Inone embodiment, controller 1253 is communicably coupled to modem 1254via communication path 1256. Communication path 1256 enables controller1253 and modem 1254 to exchange communications (e.g., messages). In oneembodiment, controller 1253 is part of ASM 1251 that includes aperture1252.

In one embodiment, controller 1253 is operable to obtain a valuerepresenting a maximum allowed PSD for the scan and skew of theaperture, determine an allowable modem power based on the valuerepresenting a maximum allowed PSD, and send an indication of theallowable modem output power to the modem. In one embodiment, theallowable modem output power is the maximum allowable modem outputpower, such that the maximum allowed PSD is not exceeded by the antennaif the maximum allowable modem output power is not exceeded by the modemduring transmissions from the antenna. In one embodiment, the allowablemodem power is determined without communication with a hub in asatellite communication system in which the antenna transmits satellitecommunications. In one embodiment, the maximum PSD value is that whichmeets a regulatory limit.

After determining the allowable modem output power, controller 1253sends the indication of the allowable modem output power to the modem bysending a single message on communication path 1256 from ASM 1251 tomodem 1254.

In response to the maximum allowable modem output power, modem 1254controls the power it outputs on modem power 1255 to aperture 1252 ofASM 1251 to remain at or below the maximum allowable modem output power.By doing so, antenna 1250 is ensured of operating within the regulatorylimits.

The following is one embodiment of a process for calculating the modemmaximum power.

-   -   1. From the theta that is recorded in the ASM, and the skew that        is derived from the latitude and longitude of the ASM and the        geolocation of the satellite, a maximum PSD from the PSD table        is derived. As an example, if FCC compliance applies, with a        theta of 35 and a skew of 20, Table 2 below is used to obtain a        maximum PSD.

TABLE 2 Skew (deg) 0 5 10 15 20 25 30 35 40 45 scan 0 15.7 14.7 14.013.5 13.5 14.0 14.3 14.1 13.3 13.8 (deg) 5 15.8 15.8 15.6 15.0 14.1 13.914.5 14.8 14.6 14.9 10 16.3 16.3 16.3 15.2 14.0 13.8 14.3 14.4 15.2 15.215 16.2 16.2 15.0 14.6 14.2 14.2 14.3 15.0 15.1 15.1 20 16.2 16.1 14.913.8 13.5 13.1 13.4 13.9 14.6 15.2 25 16.2 16.2 15.4 14.4 13.6 13.3 13.514.0 14.7 14.8 30 15.5 15.1 15.0 14.3 13.6 13.3 13.5 13.3 14.1 14.7 3516.0 16.0 15.0 13.7

12.4 12.2 12.1 12.9 14.4 40 16.6 16.5 15.6 14.4 13.2 12.4 11.9 12.0 12.813.5 45 15.8 16.3 16.6 15.3 14.0 13.1 12.7 13.0 13.0 13.4 50 16.0 16.015.8 15.5 15.2 14.2 13.7 13.4 13.2 13.0 55 15.8 15.1 14.4 13.7 12.8 12.211.6 11.3 11.2 11.3 60 12.2 12.1 11.9 11.7 11.6 11.1 10.0 9.1 8.9 9.4 6514.1 14.3 14.2 13.6 12.7 11.6 10.6 9.4 8.4 7.7 70 15.5 15.0 14.5 13.512.4 11.4 10.0 8.7 7.5 6.5 75 14.6 14.9 14.6 13.4 12.4 10.9 9.5 8.2 6.85.6 Skew (deg) 50 55 60 65 70 75 80 85 90 scan 0 14.9 15.1 15.2 15.014.9 15.3 15.1 14.5 14.3 (deg) 5 14.4 14.1 14.8 14.9 14.9 14.9 14.8 14.213.5 10 14.7 14.4 14.3 14.6 14.9 14.8 15.0 14.8 14.9 15 14.8 14.5 14.714.6 14.7 14.7 14.7 14.6 14.5 20 15.2 14.9 14.4 14.2 14.2 14.1 13.9 14.114.1 25 14.4 14.0 13.4 12.7 12.7 13.0 13.1 13.3 13.5 30 14.7 13.8 13.312.8 12.6 12.6 12.6 12.7 12.7 35 14.0 13.0 12.1 11.9 12.1 11.5 11.5 11.912.0 40 14.0 12.8 11.6 10.8 10.8 10.7 10.6 11.4 12.0 45 13.5 12.9 11.210.0 9.6 9.8 10.5 11.2 11.3 50 12.7 12.5 11.3 9.5 8.3 8.2 8.3 9.8 10.255 12.1 11.8 10.5 8.2 7.2 7.3 7.7 8.5 8.7 60 10.2 10.7 10.1 7.9 5.9 5.75.5 6.7 7.0 65 7.5 7.5 8.3 8.1 5.6 4.3 4.4 5.6 6.1 70 5.6 5.2 5.7 7.26.7 4.7 3.9 3.9 4.9 75 4.5 4.1 4.7 6.2 4.8 3.2 2.6 3.2 3.1

-   -   2. The maximum PSD for the scenario is 12.9 dBW/4 kHz. By        obtaining the current symbol rate from the modem, a maximum        power also known as effective isotropic radiated power (EIRP) at        the output of the aperture is derived. In one embodiment, the        modem provides the symbol rate to a controller in the ASM via        one or more messages (e.g., one or more OpenAMIP messages). For        this example, it is a 1 MSym carrier. Therefore, the EIRP equals        12.9 plus 10*log(1000/4), which equals 36.88 dBW. In one        embodiment, the symbol rate is maintained as constant under        network control.    -   3. The antenna gain is calculated from known performance        parameters (with some margin in one embodiment). One example        antenna has a gain of 33.5 plus 12*log(cos(theta)), which is        33.5 plus 12*log(cos(35)) and, thus the antenna gain equals        32.46 dBi.    -   4. Subtracting the antenna gain from EIRP gives a maximum BUC        power in dBW. In the example, the BUC power equals 36.88 minus        32.46, which equals 2.34 dBW or approximately 1.7 W.    -   5. From the power transfer curve of FIG. 10 (in this example)        (now with specific values included), a maximum modem power may        be derived using the maximum BUC power. For this example, assume        the modem power that correlates to a BUC output power of 2.34        dBW is −5 dBm.    -   6. The modem power (e.g., −5 dBm) is passed to the modem as a do        not exceed power level. In one embodiment, the modem power is        sent as a single message. In one embodiment, if theta changes        significantly, a new power is calculated using the method above.        If the modem does not exceed this level and the symbol rate does        not change, this will ensure the PSD limit is not exceeded        through an automatic uplink power control process while not        needing to have two-way communication with the modem and/or the        hub, which makes the UPC process to be more modem agnostic. Any        modem vendor may adhere to this as long as they are able to        receive the message and understand how to incorporate the        limit(s) into their network management algorithm.

FIG. 13 is a flow diagram of one embodiment of a process described abovefor determining the allowable modem power. In one embodiment, theprocess is performed by processing logic that may comprise hardware(circuitry, dedicated logic, etc.), software (e.g., software running ona chip), firmware, or a combination of the three. In one embodiment,this process is performed by a controller in an ASM of the terminal.

Referring to FIG. 13, the process begins by processing logic determiningan Equivalent Isotropic Radiated Power (EIRP) (processing block 1301)and obtaining an antenna gain (processing block 1302). In oneembodiment, obtaining the antenna gain comprises calculating the antennagain based on theta.

Based on the EIRP and the antenna gain, processing logic determines amaximum BUC power (processing block 1303). In one embodiment,determining the maximum BUC power based on the EIRP and the antenna gaincomprises subtracting the antenna gain from the EIRP.

With the maximum operable BUC power, processing logic determines amaximum modem output power based on the maximum operable BUC power(processing block 1304). In one embodiment, determining the maximum(operable) modem output power is based on a power transfer curve of theBUC power to modem power relationship.

Once the maximum modem output power has been determined based on themaximum (operable) BUC power, processing logic sends to the modem theindication of the maximum modem output power that can be used. In oneembodiment, processing logic sends a single message from an ASM of theterminal to the modem to indicate the maximum modem output power to themodem.

FIG. 14 illustrates a data flow diagram depicting a UPC process. In oneembodiment, the process is performed by processing logic that maycomprise hardware (circuitry, dedicated logic, etc.), software (e.g.,software running on a chip), firmware, or a combination of the three. Inone embodiment, the process is performed by software running in thedifferent units.

Referring to FIG. 14, ASM 1453 collects the modem power to BUC powerrelationship using the BUC power received from the BUC on a BUC powertelemetry line 1472 and using modem power 1460 from modem 1451. Notethat in another embodiment, the modem power-to-BUC power relationship isprovided to ASM 1453 after it has been determined for the terminal.

In response to this information, ASM 1453 determines a value of theallowed maximum output power 1461 for modem 1451 based on the operatingtheta and skew of an antenna aperture of ASM 1453 and passes that valueto modem 1451. In one embodiment, the allowed maximum output power isdetermined based on the symbol rate of the carrier on whichtransmissions from the terminal are being made. In one embodiment, ASM1453 sends a message to modem 1451 (not actual output power) that wouldbe the limit of modem 1451 to ensure that the terminal's output power(or density depending on embodiment) does not exceed regulatory limitssince the gain of BUC 1452, cable loss, and gain of the antenna apertureof ASM 1453 are known.

In response to the allowed maximum output power value, modem 1451controls its output power 1471 such that its allowed maximum modemoutput power is not exceeded, thereby ensuring that the PSD limit is notexceeded. In one embodiment, power 1471 output from modem 1451 is at theIF (intermediate frequency) before reaching BUC 1452, where it is thenupconverted and amplified to the correct band (e.g., sub-Ku band, etc.)and the desired output power level and then directed to ASM 1453 fortransmission. In one embodiment, the power at the output of modem 1471is calculated so it is the power at the output of the terminal does notexceed the PSD limit.

In one embodiment, a controller (e.g., a controller in ASM 1453)determines the allowable modem power by, as described above, determiningan Equivalent Isotropic Radiated Power (EIRP), obtaining an antennagain, determining a maximum BUC power based on the EIRP and the antennagain, and determining a maximum modem output power based on the maximumBUC power. In one embodiment, the controller obtains the antenna gain bycalculating the antenna gain based on theta. In one embodiment, thecontroller determines the maximum BUC power based on the EIRP and theantenna gain by subtracting the antenna gain from the EIRP. In oneembodiment, the controller determines the maximum modem output powerbased on the maximum BUC power using a power transfer curve of the BUCpower to modem power relationship. Using this method ensures PSDcompliance using a less complicated, easier to adopt method forautomatic UPC.

In an alternative embodiment, instead of the BUC telemetry lineproviding the BUC output power, an accurate power reader at the outputof the BUC (i.e., additional unit) may be used to determine the powerand provide it to the ASM.

In one embodiment, the modem receives all the information and determinesits maximum output power. In this case, the modem has access to the BUCoutput power. In one embodiment, this is accomplished with a telemetryline or other communication pathway directly between the modem and theBUC or via indirect that through one or more other devices. In yetanother embodiment, all the information is sent to a device other thanthe ASM and this device determines the maximum output power for themodem and sends the modem an indication of its maximum output power.

In one embodiment, if the symbol rate is not constant, then the processabove is repeated every time there is a new symbol rate or use a minimumavailable symbol rate to ensure compliance.

In one embodiment, the above process can be used to determine if thesymbol rate and/or transmit power should be changed. FIG. 15 is oneembodiment of a process for controlling an antenna. In one embodiment,the process is performed by processing logic that may comprise hardware(circuitry, dedicated logic, etc.), software (e.g., software running ona chip), firmware, or a combination of the three. In one embodiment,this process is performed by a controller on the antenna (e.g., acontroller in the ASM of the terminal).

Referring to FIG. 15, the process begins by processing logic determininga maximum allowed PSD for the skew and scan of the antenna (processingblock 1501). In one embodiment, this is performed by accessing a look uptable, such as described above, and selecting the maximum allowed PSDusing the skew and scan of the antenna.

Processing logic also receives a symbol rate and modem transmit powerfrom the modem (processing block 1502). In one embodiment, thisinformation is sent from the modem in one or more messages (e.g.,OpenAMIP messages).

Based on the symbol rate and modem transmit power, processing logiccalculates a current PSD of the antenna (processing block 1503) andcompares it to the maximum allowed PSD (processing block 1504). In oneembodiment, processing logic calculates the current PSD using thetechnique described above in FIG. 13.

Next, processing logic controls the modem to prevent transmission by theantenna at the symbol rate and transmit power if the current PSD isgreater than the maximum allowed PSD (processing block 1505). Processinglogic also requests a new symbol rate and/or modem transmit power fromthe modem and repeats the process to see if these new parameters resultin a PSD for the antenna that is at or below the maximum allowed PSD(processing block 1506). In one embodiment, processing logic obtains anew symbol rate from a schedule of symbol rates provided by, forexample, the modem. Note that this process may be repeated a number oftimes with different symbol rates and/or modem transmit powers until theantenna's PSD is at or below the maximum allowed PSD.

Other Techniques for Performing Uplink Power Control

There are a number of other embodiments for performing UPC processes byan antenna to ensure that the antenna is at or below the maximum PSD.Some features of these techniques may be used with the UPC and modemcontrol techniques described above.

In one embodiment of a UPC process, the modem determines whether tocontrol its output power based on a received maximum PSD value. In oneembodiment, the modem obtains a maximum PSD from a controller or otherdevice on the antenna (e.g., a controller or device in the ASM or acontrol board, etc.) and uses it to search another look up table (e.g.,look up tables for different space regulations, etc.) in a series oflook up tables to determine an amount of power the modem can use fortransmit and which modcods the modem should use for transmitting. Thus,the series of look up tables are used to translate the maximum PSDcommunication into a maximum modem output power.

FIG. 16 is a flow diagram of another embodiment of an uplink powercontrol process. In one embodiment, the process is performed byprocessing logic that may comprise hardware (circuitry, dedicated logic,etc.), software (e.g., software running on a chip), firmware, or acombination of the three.

Referring to FIG. 16, the process begins by processing logic setting upa look up table of maximum PSD values for the scan and skew (processingblock 1681). Next, processing logic computes a pointing solution andproduces theta and skew values (processing block 1682). In oneembodiment, this is performed according to a periodic timer 1690. Usingthe theta and skew values, processing logic looks up the maximum PSD inthe look up table (processing block 1683) and sends the identifiedmaximum PSD to modem 1685 (processing block 1684). In one embodiment,the maximum PSD is sent to the modem according to a periodic timer 1691.In response to the maximum PSD, the modem controls its output power(e.g., mute/unmute; reduce/increase transmit power, etc.).

FIG. 17 is a sequence diagram of a UPC process involving a modem and hubin a satellite communication system. Referring to FIG. 17, the ASM 1751passes the PSD maximum value to modem 1752. In one embodiment, thisoccurs at startup time for the antenna. In response to the maximum PSDvalue, modem 1752 attempts to join the communication network whilestaying within the PSD maximum, while the hub advertises a carrier forantenna terminals. Modem 1752 also sends the satellite ID and/orlongitude to ASM 1751 via a message (e.g., an OpenAMIP message) to ASM1751. Thereafter, hub 1753 sends an acknowledgement and confirmationthat modem 1752 has been joined the network.

After joining the network, ASM 1751 calculates expected scan and skewangles from the latitude, longitude, and altitude (LLA) and thesatellite. ASM 1751 also determines the “margin” for expected motion ofthe antenna and adds that to the expected PSD maximum from a look uptable before passing the value to modem 1752 via a message (e.g., anOpenAMIP ‘w’ message).

In response to the PSD maximum value, modem 1752 calculates the expectedsignal-to-noise ratio (SNR) at hub 1753 using a G/T table and PSDmaximum value provided by ASM 1751. Modem 1752 also calculates the SNRdelta improvement from expected operational SNR to adjust the PSD to thecorrect value. For example, if a PSD of 11 dBW/4 kHz is expected to bean SNR of 5 dB, then if the PSD must be 10 dBW/4 kHz the modem will lookfor a hub SNR of 4 dB.

Once the calculations have been performed, modem 1752 informs hub 1753of the estimated SNR at which it is capable of operating. In responsethereto, hub 1753 acknowledges and assigns new carriers for optimalperformance and sends the new carrier parameters to modem 1752. Modem1752 synchronizes with the new carrier and the PSD maximum value ispreloaded into modem 1752. The PSD maximum value versus scan/skew angletable is also preloaded into ASM 1751. ASM 1751 sends modem 1752 a mutecommand if the expected motion profile is exceeded. In one embodiment,ASM 1751 sends modem 1752 a mute command via a message (e.g., a viaOpenAMIP message).

Note that in one embodiment, an antenna manufacturer fully characterizesbeam patterns for any applicable scan and skew conditions and generatesa table of skew conditions versus maximum PSD allowable to remaincompliant.

In another embodiment, a multi-dimensional table (scan, skew,polarization, and regulatory environment) is used to look up maximumPSD.

In one embodiment, Link Budget Analysis (LBA) is used to estimatereference C/N, which represents performance of the link under worst casePSD max conditions. This mode is used for initially joining the networkwhen the terminal does not know its scan and skew conditions, and itguarantees compliance at very low link efficiency. Once the remote joinsthe network, it checks its current scan and skew conditions, looks up amaximum PSD value in a PSD table and passes the appropriate value overthe air to a hub modem. The hub modem compares this value to a referenceand determines how much headroom is available. Based on thatdetermination, the hub modem then commands the terminal to add a deltaamount of power (e.g., an increase in power), thereby improving linkefficiency as a result of higher C/N and higher modcod.

In one embodiment, table look ups to identify a maximum PSD value occurat regular intervals. In one embodiment, this process of table lookup isrepeated every 2 seconds.

In one embodiment, another PSD look-up table is added into the antennaterminal software where the two-dimensional table (scan and skew vs. PSDmaximum) is broken down into a one-dimensional table referred to hereinas a “pseudo-skew” table. This pseudo-skew can then leverage acommunication interface (e.g., an OpenAMIP interface) to communicatewith the network operator at high speed.

As seen in tables for FCC and ITU jurisdictions, different power levelsare allowed in different parts of the world with different satelliteenvironments. In one embodiment, to obtain the correct table for thelocation in which a satellite antenna is operating, the satelliteantenna identifies the jurisdiction in which it resides. This may occurby sending or receiving information about the jurisdiction through oneor more messages.

In one embodiment, there are two tables of suggested PSD margin for 5and 10-degree maximum displacement due to platform motion. These tablesare typically created by a network operator. In one embodiment, thevalues are generated by taking the largest delta between the PSD maximumvalue of each cell and its 5°/10° neighbors.

In one embodiment, the network operator is responsible for determining,on a regional basis, the PSD limit for a terminal. FIG. 18 illustratesan example of PSD limits for different regions. It is the responsibilityof the network operator to ensure that terminals only operate in theproper region for the set limit, and the software in the hub and theterminal modem are responsible for selecting a new limit when theterminal changes regions. This is advantageous over methods that have asingle limit set for the entire network because terminals within certainregions could obtain higher uplink throughput if the local limit couldbe higher than the worst case current global limit.

In one embodiment, run-time calculations of the current transmitted PSDare performed based on symbol rate and transmitter power, and themaximum PSD is determined by looking up the value in a table based upontheta and skew. In one embodiment, if the current PSD exceeds the PSDlimit, the terminal is muted. In one embodiment, the predefinedoperating range having a minimum and maximum PSD is determined asdescribed above but the decision to mute happens locally in the ASMinstead of in the hub. This is advantageous over implementations that donot actually know what the current PSD value is, and therefore assumesthe worst. By knowing the actual PSD value, the terminal can be allowedto raise the power beyond what would be possible now.

FIG. 19 is a flow diagram of a UPC process that performs a muteoperation to mute the terminal based on theta, skew, and bandwidth. Inone embodiment, the process is performed by processing logic that maycomprise hardware (circuitry, dedicated logic, etc.), software (e.g.,software running on a chip), firmware, or a combination of the three.Referring to FIG. 19, modem 1901 sends the symbol rate 1910 to ASM 1902.In response to symbol rate 1910, ASM 1902 calculates the current PSDbased on the symbol rate and transmit power (processing block 1911). Inone embodiment, the transmit power is derived from a BUC that receivesthe modem output power. In another embodiment, the transmit power isprovided by modem 1901. ASM 1902 also determines whether to mute orunmute modem 1901 by comparing the calculated current PSD value with themaximum PSD allowed for the current theta and skew (processing block1912). In one embodiment, the maximum PSD value per theta and skew pairis retrieved from the preloaded PSD tables. Based on the result of thedetermination of whether to mute or unmute modem 1901, ASM 1902 sends acommand 1913 telling the modem 1901 to mute or unmute its output power.

In one embodiment, the ASM performs power control based on theta, skew,and transmit (Tx) bandwidth. In one embodiment of this power controlprocess, runtime calculations of the current transmitted PSD areperformed based on symbol rate and transmit power, and the maximum PSDis determined by looking up the value in a table based upon theta andskew. If the current PSD exceeds the PSD limit, the modem power iscontrolled via a programmatic interface to reduce the power to be belowthe PSD limit. In one embodiment, the predefined operating range isdetermined as described above but the decision to control the modempower happens locally in the ASM instead of in the hub. This isadvantageous over implementations that do not actually know what thecurrent PSD value is, and therefore assumes the worst. By knowing theactual PSD value, the terminal is allowed to raise the power beyond whatwould be possible now and enables graceful degradation of performanceinstead of simply muting.

FIG. 20 is a flow diagram of a UPC process that performs modem powercontrol based on theta, skew, and bandwidth. In one embodiment, theprocess is performed by processing logic that may comprise hardware(circuitry, dedicated logic, etc.), software (e.g., software running ona chip), firmware, or a combination of the three. Referring to FIG. 20,modem 2001 sends the symbol rate 2010 to ASM 2002. In response to symbolrate 2010, ASM 2002 calculates the current PSD based on the symbol rateand transmit power (processing block 2011). In one embodiment, thetransmit power is derived from a BUC that receives the modem outputpower. In another embodiment, the transmit power is proved by modem2001. ASM 2002 also determines whether to mute or unmute modem 2001 bycomparing the calculated current PSD value with the maximum PSD allowedfor the current theta and skew (processing block 2012). In oneembodiment, the maximum PSD value per theta and skew pair is retrievedfrom the preloaded PSD tables. Based on the result of the determinationof whether to mute or unmute modem 2001, ASM 2002 sends a command tocontrol power (2013) to modem 2001. In one embodiment, this command mayinstruct the modem to increase or decrease its output power.

In one embodiment, per-terminal PSD thresholds, both minimum andmaximum, are used. This allows for a muting based solution and isadvantageous over the implementations that have a single PSD limit valueset at installation time where that value is the same for all terminals.

FIG. 21 is a flow diagram of a UPC process that controls a muteoperation based on PSD thresholds. In one embodiment, the process isperformed by processing logic that may comprise hardware (circuitry,dedicated logic, etc.), software (e.g., software running on a chip),firmware, or a combination of the three. Referring to FIG. 21, modem2101 sends the symbol rate 2110 to ASM 2102. In response to symbol rate2110, ASM 2102 calculates the current PSD based on the symbol rate andtransmit power (processing block 2111). In one embodiment, the transmitpower is derived from a BUC that receives the modem output power. Inanother embodiment, the transmit power is proved by modem 2101. ASM 2102also determines whether to mute or unmute modem 2101 by comparing thecalculated current PSD value with the maximum PSD allowed for thecurrent theta and skew (processing block 2112). In one embodiment, themaximum PSD value per theta and skew pair is retrieved from thepreloaded PSD tables. Based on the result of the determination ofwhether to mute or unmute modem 2101, ASM 2102 sends a command 2113telling the modem 2101 to mute or unmute its output power.

In one embodiment, instead of using a PSD limit determined from a settable (per terminal type), the PSD limit is defined by the networkoperator on a per-terminal basis. In one embodiment, this is used as amuting threshold. To achieve this, the worst-case symbol rate andworst-case power can be entered into the ASM. This can be used tocalculate worst-case PSD. From there, the worst-case PSD can be comparedwith the current PSD limit to determine if the ASM should mute or not.In an alternative embodiment, the worst-case symbol rate is entered butthe current output power at run time is obtained from either the modem,BUC, or external sensor. This is advantageous as it allows the use ofhigher power in areas where the network operator determines that this ispossible.

FIG. 22 is a flow diagram of a UPC process that uses worst-case valuesas describe above. In one embodiment, the process is performed byprocessing logic that may comprise hardware (circuitry, dedicated logic,etc.), software (e.g., software running on a chip), firmware, or acombination of the three. Referring to FIG. 22, ASM 2202 receives aworst-case symbol rate and power 2210 from an installer that providesthe information based on the PSD limit 2211 received from a NOC. Usingthe worst-case symbol rate and power, ASM 2202 calculates the worst-casePSD limit (processing 2212). ASM 2202 obtains symbol rate 2213 frommodem 2201. Using the calculated worst case PSD limit 2212 and symbolrate 2213, processing logic in ASM 2202 calculates the current PSD basedon symbol rate and transmit power (processing block 2214). In oneembodiment, the transmit power is derived from a BUC that receives themodem output power. In another embodiment, the transmit power is provedby modem 2201. Based on the calculated result, processing logic in theASM 2202 determines if the calculated PSD exceeds the maximum PSDallowed for this terminal type (processing block 2215). Based on theresults of the comparison, ASM 2202 performs power control on modem 2201using a command 2216.

In one embodiment, the antenna uses a database of maximum PSD values tocontrol modem output power to ensure that the antenna remains with thePSD limit. In one embodiment, this database has a per satellite or perbeam worst-case symbol rate. In one embodiment, the database is enteredby the user via graphical user interface (GUI) or script, and/or isautomatically updated via over-the-air (OTA) service. This isadvantageous as it allows the use of higher power in areas where theruntime dynamic worst-case is better than the static global worst-case.

FIG. 23 is a flow diagram of a UPC process that uses database of PSDmaximum values. In one embodiment, the process is performed byprocessing logic that may comprise hardware (circuitry, dedicated logic,etc.), software (e.g., software running on a chip), firmware, or acombination of the three. Referring to FIG. 23, modem 2301 sends thesymbol rate 2310 to ASM 2302. In response thereto, ASM 2302 calculatesthe current PSD based on the symbol rate and transmit power (processingblock 2311). In one embodiment, the transmit power is derived from a BUCthat receives the modem output power. In another embodiment, thetransmit power is proved by modem 2301. ASM 2302 also receives themaximum PSD value 2312 from database 2313. In one embodiment, themaximum PSD values in database 2313 are received as maximum PSD 2315from an installer 2314. Using the calculated current PSD value and themaximum PSD value 2312, processing logic in ASM 2302 determines if thecurrent PSD exceeds the maximum PSD (processing block 2316) and performspower control by sending a power control command 2317 to modem 2301.

In one embodiment, by collecting metrics over time from the terminals(e.g., metrics for ASM, modem, BUC, etc.) and the hub, an analysis ofhistorical data can be performed to determine better power limits for aterminal. In one embodiment, the ASM retrieves the latest limits via anover-the-air (OTA) service, and these limits can be used for mutingthresholds. In one embodiment, other UPC methods are used during theinitial data collection. This includes leveraging data collection fromother networks. This is advantageous as it provides a continuallyoptimizing solution instead of a static solution.

FIG. 24 is a flow diagram of a UPC process that is optimized using dataanalysis. In one embodiment, the process is performed by processinglogic that may comprise hardware (circuitry, dedicated logic, etc.),software (e.g., software running on a chip), firmware, or a combinationof the three. Referring to FIG. 24, modem 2401 sends symbol ate 2410 toASM 2402. In response thereto, ASM 2402 calculates the current PSD basedon the symbol rate and transmit power (processing block 2411). In oneembodiment, the transmit power is derived from a BUC that receives themodem output power. In another embodiment, the transmit power is provedby modem 2401. ASM 2402 also receives the maximum PSD value 2412 from adatabase accessible via cloud 2413 ASM 2402 receives maximum PSD value2412 from a cloud-based location 2413. The cloud base location performsbig data analysis to determine the maximum PSD dynamically using metrics2415 corresponding to antenna terminals 2414 and metrics 2417corresponding to hub 2416. Using the calculated current PSD value andthe maximum PSD value 2412, processing logic in ASM 2402 determines ifthe current PSD exceeds the maximum PSD (processing block 2418) andperforms power control by sending a power control command 2419 to modem2401.

Note that features of several of the above-describe UPC processes arecombined. Thus, a number of methods are disclosed that can allow higherpower output from the antenna or operation in regions where operationwould have been prevented previously when used with a non-parabolicantenna.

Examples of Antenna Embodiments

The techniques described above may be used with flat panel antennas.Embodiments of such flat panel antennas are disclosed. The flat panelantennas include one or more arrays of antenna elements on an antennaaperture. In one embodiment, the antenna elements comprise liquidcrystal cells. In one embodiment, the flat panel antenna is acylindrically fed antenna that includes matrix drive circuitry touniquely address and drive each of the antenna elements that are notplaced in rows and columns. In one embodiment, the elements are placedin rings.

In one embodiment, the antenna aperture having the one or more arrays ofantenna elements is comprised of multiple segments coupled together.When coupled together, the combination of the segments form closedconcentric rings of antenna elements. In one embodiment, the concentricrings are concentric with respect to the antenna feed.

Examples of Antenna Systems

In one embodiment, the flat panel antenna is part of a metamaterialantenna system. Embodiments of a metamaterial antenna system forcommunications satellite earth stations are described. In oneembodiment, the antenna system is a component or subsystem of asatellite earth station (ES) operating on a mobile platform (e.g.,aeronautical, maritime, land, etc.) that operates using either Ka-bandfrequencies or Ku-band frequencies for civil commercial satellitecommunications. Note that embodiments of the antenna system also can beused in earth stations that are not on mobile platforms (e.g., fixed ortransportable earth stations).

In one embodiment, the antenna system uses surface scatteringmetamaterial technology (e.g., antenna elements) to form and steertransmit and receive beams through separate antennas. In one embodiment,the antenna systems are analog systems, in contrast to antenna systemsthat employ digital signal processing to electrically form and steerbeams (such as phased array antennas).

In one embodiment, the antenna system is comprised of three functionalsubsystems: (1) a wave guiding structure consisting of a cylindricalwave feed architecture; (2) an array of wave scattering metamaterialunit cells that are part of antenna elements; and (3) a controlstructure to command formation of an adjustable radiation field (beam)from the metamaterial scattering elements using holographic principles.

Antenna Elements

FIG. 25 illustrates the schematic of one embodiment of a cylindricallyfed holographic radial aperture antenna. Referring to FIG. 25, theantenna aperture has one or more arrays 601 of antenna elements 603 thatare placed in concentric rings around an input feed 602 of thecylindrically fed antenna. In one embodiment, antenna elements 603 areradio frequency (RF) resonators that radiate RF energy. In oneembodiment, antenna elements 603 comprise both Rx and Tx irises that areinterleaved and distributed on the whole surface of the antennaaperture. Examples of such antenna elements are described in greaterdetail below. Note that the RF resonators described herein may be usedin antennas that do not include a cylindrical feed.

In one embodiment, the antenna includes a coaxial feed that is used toprovide a cylindrical wave feed via input feed 602. In one embodiment,the cylindrical wave feed architecture feeds the antenna from a centralpoint with an excitation that spreads outward in a cylindrical mannerfrom the feed point. That is, a cylindrically fed antenna creates anoutward travelling concentric feed wave. Even so, the shape of thecylindrical feed antenna around the cylindrical feed can be circular,square or any shape. In another embodiment, a cylindrically fed antennacreates an inward travelling feed wave. In such a case, the feed wavemost naturally comes from a circular structure.

In one embodiment, antenna elements 603 comprise irises and the apertureantenna of FIG. 25 is used to generate a main beam shaped by usingexcitation from a cylindrical feed wave for radiating irises throughtunable liquid crystal (LC) material. In one embodiment, the antenna canbe excited to radiate a horizontally or vertically polarized electricfield at desired scan angles.

In one embodiment, the antenna elements comprise a group of patchantennas. This group of patch antennas comprises an array of scatteringmetamaterial elements. In one embodiment, each scattering element in theantenna system is part of a unit cell that consists of a lowerconductor, a dielectric substrate and an upper conductor that embeds acomplementary electric inductive-capacitive resonator (“complementaryelectric LC” or “CELL”) that is etched in or deposited onto the upperconductor. As would be understood by those skilled in the art, LC in thecontext of CELC refers to inductance-capacitance, as opposed to liquidcrystal.

In one embodiment, a liquid crystal (LC) is disposed in the gap aroundthe scattering element. This LC is driven by the direct driveembodiments described above. In one embodiment, liquid crystal isencapsulated in each unit cell and separates the lower conductorassociated with a slot from an upper conductor associated with itspatch. Liquid crystal has a permittivity that is a function of theorientation of the molecules comprising the liquid crystal, and theorientation of the molecules (and thus the permittivity) can becontrolled by adjusting the bias voltage across the liquid crystal.Using this property, in one embodiment, the liquid crystal integrates anon/off switch for the transmission of energy from the guided wave to theCELC. When switched on, the CELC emits an electromagnetic wave like anelectrically small dipole antenna. Note that the teachings herein arenot limited to having a liquid crystal that operates in a binary fashionwith respect to energy transmission.

In one embodiment, the feed geometry of this antenna system allows theantenna elements to be positioned at forty-five-degree (45°) angles tothe vector of the wave in the wave feed. Note that other positions maybe used (e.g., at 40° angles). This position of the elements enablescontrol of the free space wave received by or transmitted/radiated fromthe elements. In one embodiment, the antenna elements are arranged withan inter-element spacing that is less than a free-space wavelength ofthe operating frequency of the antenna. For example, if there are fourscattering elements per wavelength, the elements in the 30 GHz transmitantenna will be approximately 2.5 mm (i.e., ¼th the 10 mm free-spacewavelength of 30 GHz).

In one embodiment, the two sets of elements are perpendicular to eachother and simultaneously have equal amplitude excitation if controlledto the same tuning state. Rotating them +/−45 degrees relative to thefeed wave excitation achieves both desired features at once. Rotatingone set 0 degrees and the other 90 degrees would achieve theperpendicular goal, but not the equal amplitude excitation goal. Notethat 0 and 90 degrees may be used to achieve isolation when feeding thearray of antenna elements in a single structure from two sides.

The amount of radiated power from each unit cell is controlled byapplying a voltage to the patch (potential across the LC channel) usinga controller. Traces to each patch are used to provide the voltage tothe patch antenna. The voltage is used to tune or detune the capacitanceand thus the resonance frequency of individual elements to effectuatebeam forming. The voltage required is dependent on the liquid crystalmixture being used. The voltage tuning characteristic of liquid crystalmixtures is mainly described by a threshold voltage at which the liquidcrystal starts to be affected by the voltage and the saturation voltage,above which an increase of the voltage does not cause major tuning inliquid crystal. These two characteristic parameters can change fordifferent liquid crystal mixtures.

In one embodiment, as discussed above, a matrix drive is used to applyvoltage to the patches in order to drive each cell separately from allthe other cells without having a separate connection for each cell(direct drive). Because of the high density of elements, the matrixdrive is an efficient way to address each cell individually.

In one embodiment, the control structure for the antenna system has 2main components: the antenna array controller, which includes driveelectronics, for the antenna system, is below the wave scatteringstructure, while the matrix drive switching array is interspersedthroughout the radiating RF array in such a way as to not interfere withthe radiation. In one embodiment, the drive electronics for the antennasystem comprise commercial off-the shelf LCD controls used in commercialtelevision appliances that adjust the bias voltage for each scatteringelement by adjusting the amplitude or duty cycle of an AC bias signal tothat element.

In one embodiment, the antenna array controller also contains amicroprocessor executing the software. The control structure may alsoincorporate sensors (e.g., a GPS receiver, a three-axis compass, a3-axis accelerometer, 3-axis gyro, 3-axis magnetometer, etc.) to providelocation and orientation information to the processor. The location andorientation information may be provided to the processor by othersystems in the earth station and/or may not be part of the antennasystem.

More specifically, the antenna array controller controls which elementsare turned off and those elements turned on and at which phase andamplitude level at the frequency of operation. The elements areselectively detuned for frequency operation by voltage application.

For transmission, a controller supplies an array of voltage signals tothe RF patches to create a modulation, or control pattern. The controlpattern causes the elements to be turned to different states. In oneembodiment, multistate control is used in which various elements areturned on and off to varying levels, further approximating a sinusoidalcontrol pattern, as opposed to a square wave (i.e., a sinusoid grayshade modulation pattern). In one embodiment, some elements radiate morestrongly than others, rather than some elements radiate and some do not.Variable radiation is achieved by applying specific voltage levels,which adjusts the liquid crystal permittivity to varying amounts,thereby detuning elements variably and causing some elements to radiatemore than others.

The generation of a focused beam by the metamaterial array of elementscan be explained by the phenomenon of constructive and destructiveinterference. Individual electromagnetic waves sum up (constructiveinterference) if they have the same phase when they meet in free spaceand waves cancel each other (destructive interference) if they are inopposite phase when they meet in free space. If the slots in a slottedantenna are positioned so that each successive slot is positioned at adifferent distance from the excitation point of the guided wave, thescattered wave from that element will have a different phase than thescattered wave of the previous slot. If the slots are spaced one quarterof a guided wavelength apart, each slot will scatter a wave with a onefourth phase delay from the previous slot.

Using the array, the number of patterns of constructive and destructiveinterference that can be produced can be increased so that beams can bepointed theoretically in any direction plus or minus ninety degrees(90°) from the bore sight of the antenna array, using the principles ofholography. Thus, by controlling which metamaterial unit cells areturned on or off (i.e., by changing the pattern of which cells areturned on and which cells are turned off), a different pattern ofconstructive and destructive interference can be produced, and theantenna can change the direction of the main beam. The time required toturn the unit cells on and off dictates the speed at which the beam canbe switched from one location to another location.

In one embodiment, the antenna system produces one steerable beam forthe uplink antenna and one steerable beam for the downlink antenna. Inone embodiment, the antenna system uses metamaterial technology toreceive beams and to decode signals from the satellite and to formtransmit beams that are directed toward the satellite. In oneembodiment, the antenna systems are analog systems, in contrast toantenna systems that employ digital signal processing to electricallyform and steer beams (such as phased array antennas). In one embodiment,the antenna system is considered a “surface” antenna that is planar andrelatively low profile, especially when compared to conventionalsatellite dish receivers.

FIG. 26 illustrates a perspective view of one row of antenna elementsthat includes a ground plane and a reconfigurable resonator layer.Reconfigurable resonator layer 1230 includes an array of tunable slots1210. The array of tunable slots 1210 can be configured to point theantenna in a desired direction. Each of the tunable slots can betuned/adjusted by varying a voltage across the liquid crystal.

Control module 1280 is coupled to reconfigurable resonator layer 1230 tomodulate the array of tunable slots 1210 by varying the voltage acrossthe liquid crystal in FIG. 27. Control module 1280 may include a FieldProgrammable Gate Array (“FPGA”), a microprocessor, a controller,System-on-a-Chip (SoC), or other processing logic. In one embodiment,control module 1280 includes logic circuitry (e.g., multiplexer) todrive the array of tunable slots 1210. In one embodiment, control module1280 receives data that includes specifications for a holographicdiffraction pattern to be driven onto the array of tunable slots 1210.The holographic diffraction patterns may be generated in response to aspatial relationship between the antenna and a satellite so that theholographic diffraction pattern steers the downlink beams (and uplinkbeam if the antenna system performs transmit) in the appropriatedirection for communication. Although not drawn in each figure, acontrol module similar to control module 1280 may drive each array oftunable slots described in the figures of the disclosure.

Radio Frequency (“RF”) holography is also possible using analogoustechniques where a desired RF beam can be generated when an RF referencebeam encounters an RF holographic diffraction pattern. In the case ofsatellite communications, the reference beam is in the form of a feedwave, such as feed wave 1205 (approximately 20 GHz in some embodiments).To transform a feed wave into a radiated beam (either for transmittingor receiving purposes), an interference pattern is calculated betweenthe desired RF beam (the object beam) and the feed wave (the referencebeam). The interference pattern is driven onto the array of tunableslots 1210 as a diffraction pattern so that the feed wave is “steered”into the desired RF beam (having the desired shape and direction). Inother words, the feed wave encountering the holographic diffractionpattern “reconstructs” the object beam, which is formed according todesign requirements of the communication system. The holographicdiffraction pattern contains the excitation of each element and iscalculated by w_(hologram)=w*_(in)w_(out), with w_(in) as the waveequation in the waveguide and w_(out) the wave equation on the outgoingwave.

FIG. 27 illustrates one embodiment of a tunable resonator/slot 1210.Tunable slot 1210 includes an iris/slot 1212, a radiating patch 1211,and liquid crystal 1213 disposed between iris 1212 and patch 1211. Inone embodiment, radiating patch 1211 is co-located with iris 1212.

FIG. 28 illustrates a cross section view of one embodiment of a physicalantenna aperture. The antenna aperture includes ground plane 1245, and ametal layer 1236 within iris layer 1233, which is included inreconfigurable resonator layer 1230. In one embodiment, the antennaaperture of FIG. 28 includes a plurality of tunable resonator/slots 1210of FIG. 27. Iris/slot 1212 is defined by openings in metal layer 1236. Afeed wave, such as feed wave 1205 of FIG. 26, may have a microwavefrequency compatible with satellite communication channels. The feedwave propagates between ground plane 1245 and resonator layer 1230.

Reconfigurable resonator layer 1230 also includes gasket layer 1232 andpatch layer 1231. Gasket layer 1232 is disposed between patch layer 1231and iris layer 1233. Note that in one embodiment, a spacer could replacegasket layer 1232. In one embodiment, iris layer 1233 is a printedcircuit board (“PCB”) that includes a copper layer as metal layer 1236.In one embodiment, iris layer 1233 is glass. Iris layer 1233 may beother types of substrates.

Openings may be etched in the copper layer to form slots 1212. In oneembodiment, iris layer 1233 is conductively coupled by a conductivebonding layer to another structure (e.g., a waveguide) in FIG. 28. Notethat in an embodiment the iris layer is not conductively coupled by aconductive bonding layer and is instead interfaced with a non-conductingbonding layer.

Patch layer 1231 may also be a PCB that includes metal as radiatingpatches 1211. In one embodiment, gasket layer 1232 includes spacers 1239that provide a mechanical standoff to define the dimension between metallayer 1236 and patch 1211. In one embodiment, the spacers are 75microns, but other sizes may be used (e.g., 3-200 mm). As mentionedabove, in one embodiment, the antenna aperture of FIG. 26 includesmultiple tunable resonator/slots, such as tunable resonator/slot 1210includes patch 1211, liquid crystal 1213, and iris 1212 of FIG. 27. Thechamber for liquid crystal 1213 is defined by spacers 1239, iris layer1233 and metal layer 1236. When the chamber is filled with liquidcrystal, patch layer 1231 can be laminated onto spacers 1239 to sealliquid crystal within resonator layer 1230.

A voltage between patch layer 1231 and iris layer 1233 can be modulatedto tune the liquid crystal in the gap between the patch and the slots(e.g., tunable resonator/slot 1210). Adjusting the voltage across liquidcrystal 1213 varies the capacitance of a slot (e.g., tunableresonator/slot 1210). Accordingly, the reactance of a slot (e.g.,tunable resonator/slot 1210) can be varied by changing the capacitance.Resonant frequency of slot 1210 also changes according to the equation

$f = \frac{1}{2\pi\sqrt{LC}}$where ƒ is me resonant frequency of slot 1210 and L and C are theinductance and capacitance of slot 1210, respectively. The resonantfrequency of slot 1210 affects the energy radiated from feed wave 1205propagating through the waveguide. As an example, if feed wave 1205 is20 GHz, the resonant frequency of a slot 1210 may be adjusted (byvarying the capacitance) to 17 GHz so that the slot 1210 couplessubstantially no energy from feed wave 1205. Or, the resonant frequencyof a slot 1210 may be adjusted to 20 GHz so that the slot 1210 couplesenergy from feed wave 1205 and radiates that energy into free space.Although the examples given are binary (fully radiating or not radiatingat all), full gray scale control of the reactance, and therefore theresonant frequency of slot 1210 is possible with voltage variance over amulti-valued range. Hence, the energy radiated from each slot 1210 canbe finely controlled so that detailed holographic diffraction patternscan be formed by the array of tunable slots.

In one embodiment, tunable slots in a row are spaced from each other byλ/5. Other spacings may be used. In one embodiment, each tunable slot ina row is spaced from the closest tunable slot in an adjacent row by λ/2,and, thus, commonly oriented tunable slots in different rows are spacedby λ/4, though other spacings are possible (e.g., λ/5, λ/6.3). Inanother embodiment, each tunable slot in a row is spaced from theclosest tunable slot in an adjacent row by λk/3.

Embodiments use reconfigurable metamaterial technology, such asdescribed in U.S. patent application Ser. No. 14/550,178, entitled“Dynamic Polarization and Coupling Control from a SteerableCylindrically Fed Holographic Antenna”, filed Nov. 21, 2014 and U.S.patent application Ser. No. 14/610,502, entitled “Ridged Waveguide FeedStructures for Reconfigurable Antenna”, filed Jan. 30, 2015.

FIGS. 29A-D illustrate one embodiment of the different layers forcreating the slotted array. The antenna array includes antenna elementsthat are positioned in rings, such as the example rings shown in FIG.29A. Note that in this example the antenna array has two different typesof antenna elements that are used for two different types of frequencybands.

FIG. 29A illustrates a portion of the first iris board layer withlocations corresponding to the slots. Referring to FIG. 29A, the circlesare open areas/slots in the metallization in the bottom side of the irissubstrate, and are for controlling the coupling of elements to the feed(the feed wave). Note that this layer is an optional layer and is notused in all designs. FIG. 29B illustrates a portion of the second irisboard layer containing slots. FIG. 29C illustrates patches over aportion of the second iris board layer. FIG. 29D illustrates a top viewof a portion of the slotted array.

FIG. 30 illustrates a side view of one embodiment of a cylindrically fedantenna structure. The antenna produces an inwardly travelling waveusing a double layer feed structure (i.e., two layers of a feedstructure). In one embodiment, the antenna includes a circular outershape, though this is not required. That is, non-circular inwardtravelling structures can be used. In one embodiment, the antennastructure in FIG. 30 includes a coaxial feed, such as, for example,described in U.S. Publication No. 2015/0236412, entitled “DynamicPolarization and Coupling Control from a Steerable Cylindrically FedHolographic Antenna”, filed on Nov. 21, 2014.

Referring to FIG. 30, a coaxial pin 1601 is used to excite the field onthe lower level of the antenna. In one embodiment, coaxial pin 1601 is a50Ω coax pin that is readily available. Coaxial pin 1601 is coupled(e.g., bolted) to the bottom of the antenna structure, which isconducting ground plane 1602.

Separate from conducting ground plane 1602 is interstitial conductor1603, which is an internal conductor. In one embodiment, conductingground plane 1602 and interstitial conductor 1603 are parallel to eachother. In one embodiment, the distance between ground plane 1602 andinterstitial conductor 1603 is 0.1-0.15″. In another embodiment, thisdistance may be λ/2, where λ is the wavelength of the travelling wave atthe frequency of operation.

Ground plane 1602 is separated from interstitial conductor 1603 via aspacer 1604. In one embodiment, spacer 1604 is a foam or air-likespacer. In one embodiment, spacer 1604 comprises a plastic spacer.

On top of interstitial conductor 1603 is dielectric layer 1605. In oneembodiment, dielectric layer 1605 is plastic. The purpose of dielectriclayer 1605 is to slow the travelling wave relative to free spacevelocity. In one embodiment, dielectric layer 1605 slows the travellingwave by 30% relative to free space. In one embodiment, the range ofindices of refraction that are suitable for beam forming are 1.2-1.8,where free space has by definition an index of refraction equal to 1.Other dielectric spacer materials, such as, for example, plastic, may beused to achieve this effect. Note that materials other than plastic maybe used as long as they achieve the desired wave slowing effect.Alternatively, a material with distributed structures may be used asdielectric 1605, such as periodic sub-wavelength metallic structuresthat can be machined or lithographically defined, for example.

An RF-array 1606 is on top of dielectric 1605. In one embodiment, thedistance between interstitial conductor 1603 and RF-array 1606 is0.1-0.15″. In another embodiment, this distance may be λ_(eff)/2, whereλ_(eff) is the effective wavelength in the medium at the designfrequency.

The antenna includes sides 1607 and 1608. Sides 1607 and 1608 are angledto cause a travelling wave feed from coax pin 1601 to be propagated fromthe area below interstitial conductor 1603 (the spacer layer) to thearea above interstitial conductor 1603 (the dielectric layer) viareflection. In one embodiment, the angle of sides 1607 and 1608 are at45° angles. In an alternative embodiment, sides 1607 and 1608 could bereplaced with a continuous radius to achieve the reflection. While FIG.30 shows angled sides that have angle of 45 degrees, other angles thataccomplish signal transmission from lower level feed to upper level feedmay be used. That is, given that the effective wavelength in the lowerfeed will generally be different than in the upper feed, some deviationfrom the ideal 45° angles could be used to aid transmission from thelower to the upper feed level. For example, in another embodiment, the45° angles are replaced with a single step. The steps on one end of theantenna go around the dielectric layer, interstitial the conductor, andthe spacer layer. The same two steps are at the other ends of theselayers.

In operation, when a feed wave is fed in from coaxial pin 1601, the wavetravels outward concentrically oriented from coaxial pin 1601 in thearea between ground plane 1602 and interstitial conductor 1603. Theconcentrically outgoing waves are reflected by sides 1607 and 1608 andtravel inwardly in the area between interstitial conductor 1603 and RFarray 1606. The reflection from the edge of the circular perimetercauses the wave to remain in phase (i.e., it is an in-phase reflection).The travelling wave is slowed by dielectric layer 1605. At this point,the travelling wave starts interacting and exciting with elements in RFarray 1606 to obtain the desired scattering.

To terminate the travelling wave, a termination 1609 is included in theantenna at the geometric center of the antenna. In one embodiment,termination 1609 comprises a pin termination (e.g., a 50Ω pin). Inanother embodiment, termination 1609 comprises an RF absorber thatterminates unused energy to prevent reflections of that unused energyback through the feed structure of the antenna. These could be used atthe top of RF array 1606.

FIG. 31 illustrates another embodiment of the antenna system with anoutgoing wave. Referring to FIG. 31, two ground planes 1610 and 1611 aresubstantially parallel to each other with a dielectric layer 1612 (e.g.,a plastic layer, etc.) in between ground planes. RF absorbers 1619(e.g., resistors) couple the two ground planes 1610 and 1611 together. Acoaxial pin 1615 (e.g., 50Ω) feeds the antenna. An RF array 1616 is ontop of dielectric layer 1612 and ground plane 1611.

In operation, a feed wave is fed through coaxial pin 1615 and travelsconcentrically outward and interacts with the elements of RF array 1616.

The cylindrical feed in both the antennas of FIGS. 30 and 31 improvesthe service angle of the antenna. Instead of a service angle of plus orminus forty-five degrees azimuth (±45° Az) and plus or minus twenty-fivedegrees elevation (±25° El), in one embodiment, the antenna system has aservice angle of seventy-five degrees (75°) from the bore sight in alldirections. As with any beam forming antenna comprised of manyindividual radiators, the overall antenna gain is dependent on the gainof the constituent elements, which themselves are angle-dependent. Whenusing common radiating elements, the overall antenna gain typicallydecreases as the beam is pointed further off bore sight. At 75 degreesoff bore sight, significant gain degradation of about 25 dB is expected.

Embodiments of the antenna having a cylindrical feed solve one or moreproblems. These include dramatically simplifying the feed structurecompared to antennas fed with a corporate divider network and thereforereducing total required antenna and antenna feed volume; decreasingsensitivity to manufacturing and control errors by maintaining high beamperformance with coarser controls (extending all the way to simplebinary control); giving a more advantageous side lobe pattern comparedto rectilinear feeds because the cylindrically oriented feed wavesresult in spatially diverse side lobes in the far field; and allowingpolarization to be dynamic, including allowing left-hand circular,right-hand circular, and linear polarizations, while not requiring apolarizer.

Array of Wave Scattering Elements

RF array 1606 of FIG. 30 and RF array 1616 of FIG. 31 include a wavescattering subsystem that includes a group of patch antennas (e.g.,scatterers) that act as radiators. This group of patch antennascomprises an array of scattering metamaterial elements.

In one embodiment, each scattering element in the antenna system is partof a unit cell that consists of a lower conductor, a dielectricsubstrate and an upper conductor that embeds a complementary electricinductive-capacitive resonator (“complementary electric LC” or “CELC”)that is etched in or deposited onto the upper conductor.

In one embodiment, a liquid crystal (LC) is injected in the gap aroundthe scattering element. Liquid crystal is encapsulated in each unit celland separates the lower conductor associated with a slot from an upperconductor associated with its patch. Liquid crystal has a permittivitythat is a function of the orientation of the molecules comprising theliquid crystal, and the orientation of the molecules (and thus thepermittivity) can be controlled by adjusting the bias voltage across theliquid crystal. Using this property, the liquid crystal acts as anon/off switch for the transmission of energy from the guided wave to theCELC. When switched on, the CELC emits an electromagnetic wave like anelectrically small dipole antenna.

Controlling the thickness of the LC increases the beam switching speed.A fifty percent (50%) reduction in the gap between the lower and theupper conductor (the thickness of the liquid crystal) results in afourfold increase in speed. In another embodiment, the thickness of theliquid crystal results in a beam switching speed of approximatelyfourteen milliseconds (14 ms). In one embodiment, the LC is doped in amanner well-known in the art to improve responsiveness so that a sevenmillisecond (7 ms) requirement can be met.

The CELC element is responsive to a magnetic field that is appliedparallel to the plane of the CELC element and perpendicular to the CELCgap complement. When a voltage is applied to the liquid crystal in themetamaterial scattering unit cell, the magnetic field component of theguided wave induces a magnetic excitation of the CELC, which, in turn,produces an electromagnetic wave in the same frequency as the guidedwave.

The phase of the electromagnetic wave generated by a single CELC can beselected by the position of the CELC on the vector of the guided wave.Each cell generates a wave in phase with the guided wave parallel to theCELC. Because the CELCs are smaller than the wave length, the outputwave has the same phase as the phase of the guided wave as it passesbeneath the CELC.

In one embodiment, the cylindrical feed geometry of this antenna systemallows the CELC elements to be positioned at forty-five-degree (45°)angles to the vector of the wave in the wave feed. This position of theelements enables control of the polarization of the free space wavegenerated from or received by the elements. In one embodiment, the CELCsare arranged with an inter-element spacing that is less than afree-space wavelength of the operating frequency of the antenna. Forexample, if there are four scattering elements per wavelength, theelements in the 30 GHz transmit antenna will be approximately 2.5 mm(i.e., ¼th the 10 mm free-space wavelength of 30 GHz).

In one embodiment, the CELCs are implemented with patch antennas thatinclude a patch co-located over a slot with liquid crystal between thetwo. In this respect, the metamaterial antenna acts like a slotted(scattering) wave guide. With a slotted wave guide, the phase of theoutput wave depends on the location of the slot in relation to theguided wave.

Cell Placement

In one embodiment, the antenna elements are placed on the cylindricalfeed antenna aperture in a way that allows for a systematic matrix drivecircuit. The placement of the cells includes placement of thetransistors for the matrix drive. FIG. 32 illustrates one embodiment ofthe placement of matrix drive circuitry with respect to antennaelements. Referring to FIG. 32, row controller 1701 is coupled totransistors 1711 and 1712, via row select signals Row1 and Row2,respectively, and column controller 1702 is coupled to transistors 1711and 1712 via column select signal Column1. Transistor 1711 is alsocoupled to antenna element 1721 via connection to patch 1731, whiletransistor 1712 is coupled to antenna element 1722 via connection topatch 1732.

In an initial approach to realize matrix drive circuitry on thecylindrical feed antenna with unit cells placed in a non-regular grid,two steps are performed. In the first step, the cells are placed onconcentric rings and each of the cells is connected to a transistor thatis placed beside the cell and acts as a switch to drive each cellseparately. In the second step, the matrix drive circuitry is built inorder to connect every transistor with a unique address as the matrixdrive approach requires. Because the matrix drive circuit is built byrow and column traces (similar to LCDs) but the cells are placed onrings, there is no systematic way to assign a unique address to eachtransistor. This mapping problem results in very complex circuitry tocover all the transistors and leads to a significant increase in thenumber of physical traces to accomplish the routing. Because of the highdensity of cells, those traces disturb the RF performance of the antennadue to coupling effect. Also, due to the complexity of traces and highpacking density, the routing of the traces cannot be accomplished bycommercially available layout tools.

In one embodiment, the matrix drive circuitry is predefined before thecells and transistors are placed. This ensures a minimum number oftraces that are necessary to drive all the cells, each with a uniqueaddress. This strategy reduces the complexity of the drive circuitry andsimplifies the routing, which subsequently improves the RF performanceof the antenna.

More specifically, in one approach, in the first step, the cells areplaced on a regular rectangular grid composed of rows and columns thatdescribe the unique address of each cell. In the second step, the cellsare grouped and transformed to concentric circles while maintainingtheir address and connection to the rows and columns as defined in thefirst step. A goal of this transformation is not only to put the cellson rings but also to keep the distance between cells and the distancebetween rings constant over the entire aperture. In order to accomplishthis goal, there are several ways to group the cells.

In one embodiment, a TFT package is used to enable placement and uniqueaddressing in the matrix drive. FIG. 33 illustrates one embodiment of aTFT package. Referring to FIG. 33, a TFT and a hold capacitor 1803 isshown with input and output ports. There are two input ports connectedto traces 1801 and two output ports connected to traces 1802 to connectthe TFTs together using the rows and columns. In one embodiment, the rowand column traces cross in 90° angles to reduce, and potentiallyminimize, the coupling between the row and column traces. In oneembodiment, the row and column traces are on different layers.

An Example of a Full Duplex Communication System

In another embodiment, the combined antenna apertures are used in a fullduplex communication system. FIG. 34 is a block diagram of anotherembodiment of a communication system having simultaneous transmit andreceive paths. While only one transmit path and one receive path areshown, the communication system may include more than one transmit pathand/or more than one receive path.

Referring to FIG. 34, antenna 1401 includes two spatially interleavedantenna arrays operable independently to transmit and receivesimultaneously at different frequencies as described above. In oneembodiment, antenna 1401 is coupled to diplexer 1445. The coupling maybe by one or more feeding networks. In one embodiment, in the case of aradial feed antenna, diplexer 1445 combines the two signals and theconnection between antenna 1401 and diplexer 1445 is a single broad-bandfeeding network that can carry both frequencies.

Diplexer 1445 is coupled to a low noise block down converter (LNBs)1427, which performs a noise filtering function and a down conversionand amplification function in a manner well-known in the art. In oneembodiment, LNB 1427 is in an out-door unit (ODU). In anotherembodiment, LNB 1427 is integrated into the antenna apparatus. LNB 1427is coupled to a modem 1460, which is coupled to computing system 1440(e.g., a computer system, modem, etc.).

Modem 1460 includes an analog-to-digital converter (ADC) 1422, which iscoupled to LNB 1427, to convert the received signal output from diplexer1445 into digital format. Once converted to digital format, the signalis demodulated by demodulator 1423 and decoded by decoder 1424 to obtainthe encoded data on the received wave. The decoded data is then sent tocontroller 1425, which sends it to computing system 1440.

Modem 1460 also includes an encoder 1430 that encodes data to betransmitted from computing system 1440. The encoded data is modulated bymodulator 1431 and then converted to analog by digital-to-analogconverter (DAC) 1432. The analog signal is then filtered by a BUC(up-convert and high pass amplifier) 1433 and provided to one port ofdiplexer 1445. In one embodiment, BUC 1433 is in an out-door unit (ODU).

Diplexer 1445 operating in a manner well-known in the art provides thetransmit signal to antenna 1401 for transmission.

Controller 1450 controls antenna 1401, including the two arrays ofantenna elements on the single combined physical aperture.

The communication system would be modified to include thecombiner/arbiter described above. In such a case, the combiner/arbiterafter the modem but before the BUC and LNB.

Note that the full duplex communication system shown in FIG. 34 has anumber of applications, including but not limited to, internetcommunication, vehicle communication (including software updating), etc.

There are a number of example embodiments described herein.

Example 1 is a method for use by a terminal in a satellite communicationsystem, where the terminal has an antenna, a modem and a controller, andthe method comprises: determining the scan and skew of the antenna;obtaining, using the controller, a value representing a maximum allowedPower Spectral Density (PSD) for the determined scan and skew;determining, using the controller, a maximum allowable modem power basedon the value representing a maximum allowed PSD, the maximum allowablemodem power being that which ensures that transmissions from theterminal do not exceed the maximum allowed PSD if the maximum allowablemodem output power is not exceeded by the modem; sending, using thecontroller, an indication of the allowable modem output power to themodem; and performing one or more transmissions from the terminal basedon modem outputs in accordance with the maximum allowable modem outputpower.

Example 2 is the method of example 1 that may optionally include thatthe controller is part of an antenna subsystem module (ASM).

Example 3 is the method of example 2 that may optionally include thatthe maximum allowable modem power is determined without communicationwith a hub in the satellite communication system.

Example 4 is the method of example 1 that may optionally include thatthe maximum PSD value is that which meets a regulatory limit.

Example 5 is the method of example 1 that may optionally include thatdetermining the maximum allowable modem power comprises: determining anEquivalent Isotropic Radiated Power (EIRP); obtaining an antenna gain;determining a maximum block upconverter (BUC) output power based on theEIRP and the antenna gain; and determining the maximum modem outputpower based on the maximum BUC power.

Example 6 is the method of example 5 that may optionally include thatobtaining the antenna gain comprises calculating the antenna gain basedon elevation angle.

Example 7 is the method of example 5 that may optionally include thatdetermining the maximum BUC power based on the EIRP and the antenna gaincomprises subtracting the antenna gain from the EIRP.

Example 8 is the method of example 5 that may optionally include thatdetermining the maximum modem output power is based on a power transfercurve of the BUC power to modem power relationship.

Example 9 is the method of example 1 that may optionally include thatsending the indication comprises sending a single message from an ASM ofthe terminal to the modem.

Example 10 is a terminal for use in a satellite communication system,the terminal comprising: an aperture having radiating antenna elementsoperable to radiate radio frequency (RF) signals; a modem coupled to theaperture; a BUC coupled to the modem; and a controller coupled to themodem and the BUC and operable to obtain a value representing a maximumallowed PSD for the scan and skew of the aperture, determine a maximumallowable modem power based on the value representing a maximum allowedPSD, the maximum allowable modem power being that which ensures thattransmissions from the terminal do not exceed the maximum allowed PSD ifthe maximum allowable modem output power is not exceeded by the modem,and send an indication of the allowable modem output power to the modem,wherein the aperture transmits wirelessly based on modem outputs inaccordance with the maximum allowable modem output power.

Example 11 is the terminal of example 10 that may optionally includethat the controller is part of an antenna subsystem module (ASM) thatincludes the aperture.

Example 12 is the terminal of example 10 that may optionally includethat the maximum allowable modem power is determined withoutcommunication with a hub in a satellite communication system in whichthe aperture transmits satellite communications.

Example 13 is the terminal of example 10 that may optionally includethat the maximum PSD value is that which meets a regulatory limit.

Example 14 is the terminal of example 10 that may optionally includethat the controller determines the maximum allowable modem power by:determining an Equivalent Isotropic Radiated Power (EIRP); obtaining anantenna gain; determining a maximum BUC power based on the EIRP and theantenna gain; and determining the maximum modem output power based onthe maximum BUC power.

Example 15 is the terminal of example 14 that may optionally includethat the controller obtains the antenna gain by calculating the antennagain based on elevation angle.

Example 16 is the terminal of example 14 that may optionally includethat the controller determines the maximum BUC power based on the EIRPand the antenna gain by subtracting the antenna gain from the EIRP.

Example 17 is the terminal of example 14 that may optionally includethat the controller determines the maximum modem output power based onthe maximum BUC power using a power transfer curve of the BUC power tomodem power relationship.

Example 18 is an article of manufacture having one or morenon-transitory computer readable media storing instruction thereonwhich, when executed by a terminal having an antenna, a modem and acontroller, cause the terminal to perform a method comprising:determining the scan and skew of the antenna; obtaining, using thecontroller, a value representing a maximum allowed PSD for thedetermined scan and skew; determining, using the controller, a maximumallowable modem power based on the value representing a maximum allowedPSD, the maximum allowable modem power being that which ensures thattransmissions from the terminal do not exceed the maximum allowed PSD ifthe maximum allowable modem output power is not exceeded by the modem;sending, using the controller, an indication of the allowable modemoutput power to the modem; and performing one or more transmissions fromthe terminal based on modem outputs in accordance with the maximumallowable modem output power.

Example 19 is the article of manufacture of example 18 that mayoptionally include that determining the maximum allowable modem powercomprises: determining an Equivalent Isotropic Radiated Power (EIRP);obtaining an antenna gain; determining a maximum BUC power based on theEIRP and the antenna gain; and determining the maximum modem outputpower based on the maximum BUC power.

Example 20 is the article of manufacture of example 18 that mayoptionally include that obtaining the antenna gain comprises calculatingthe antenna gain based on elevation angle, determining the maximum BUCpower based on the EIRP and the antenna gain comprises subtracting theantenna gain from the EIRP, and determining the maximum modem outputpower is based on a power transfer curve of the BUC power to modem powerrelationship.

Some portions of the detailed descriptions above are presented in termsof algorithms and symbolic representations of operations on data bitswithin a computer memory. These algorithmic descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of steps leading to a desiredresult. The steps are those requiring physical manipulations of physicalquantities. Usually, though not necessarily, these quantities take theform of electrical or magnetic signals capable of being stored,transferred, combined, compared, and otherwise manipulated. It hasproven convenient at times, principally for reasons of common usage, torefer to these signals as bits, values, elements, symbols, characters,terms, numbers, or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the following discussion,it is appreciated that throughout the description, discussions utilizingterms such as “processing” or “computing” or “calculating” or“determining” or “displaying” or the like, refer to the action andprocesses of a computer system, or similar electronic computing device,that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The present invention also relates to apparatus for performing theoperations herein. This apparatus may be specially constructed for therequired purposes, or it may comprise a general-purpose computerselectively activated or reconfigured by a computer program stored inthe computer. Such a computer program may be stored in a computerreadable storage medium, such as, but is not limited to, any type ofdisk including floppy disks, optical disks, CD-ROMs, andmagnetic-optical disks, read-only memories (ROMs), random accessmemories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any typeof media suitable for storing electronic instructions, and each coupledto a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general-purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct more specializedapparatus to perform the required method steps. The required structurefor a variety of these systems will appear from the description below.In addition, the present invention is not described with reference toany particular programming language. It will be appreciated that avariety of programming languages may be used to implement the teachingsof the invention as described herein.

A machine-readable medium includes any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer). For example, a machine-readable medium includes read onlymemory (“ROM”); random access memory (“RAM”); magnetic disk storagemedia; optical storage media; flash memory devices; etc.

Whereas many alterations and modifications of the present invention willno doubt become apparent to a person of ordinary skill in the art afterhaving read the foregoing description, it is to be understood that anyparticular embodiment shown and described by way of illustration is inno way intended to be considered limiting. Therefore, references todetails of various embodiments are not intended to limit the scope ofthe claims which in themselves recite only those features regarded asessential to the invention.

We claim:
 1. A method for use by a terminal in a satellite communicationsystem, the terminal having an antenna, a modem, and a block upconverter(BUC) coupled to the modem, and a controller, the method comprising:determining the scan and skew of the antenna; obtaining, using thecontroller, a value representing a maximum allowed Power SpectralDensity (PSD) for the determined scan and skew; determining, using thecontroller, a maximum allowable modem output power based on the valuerepresenting a maximum allowed PSD and based on a power transfer curveof a BUC power to modem power relationship, the maximum allowable modemoutput power being that which ensures that transmissions from theterminal do not exceed the maximum allowed PSD if the maximum allowablemodem output power is not exceeded by the modem; sending, using thecontroller, an indication of the maximum allowable modem output power tothe modem; and performing one or more transmissions from the terminalbased on modem output power in accordance with the maximum allowablemodem output power.
 2. The method defined in claim 1 wherein thecontroller is part of an antenna subsystem module (ASM).
 3. The methoddefined in claim 1 wherein the maximum allowable modem output power isdetermined without communication with a hub in the satellitecommunication system.
 4. The method defined in claim 1 wherein themaximum PSD value is that which meets a regulatory limit.
 5. The methoddefined in claim 1 wherein determining the maximum allowable modemoutput power comprises: determining an Equivalent Isotropic RadiatedPower (EIRP); obtaining an antenna gain; determining a maximum blockupconverter (BUC) output power based on the EIRP and the antenna gain;and determining the maximum allowable modem output power based on themaximum BUC output power.
 6. The method defined in claim 5 whereinobtaining the antenna gain comprises calculating the antenna gain basedon elevation angle.
 7. The method defined in claim 5 wherein determiningthe maximum BUC output power based on the EIRP and the antenna gaincomprises subtracting the antenna gain from the EIRP.
 8. The methoddefined in claim 1 wherein sending the indication comprises sending asingle message from an ASM of the terminal to the modem.
 9. A terminalfor use in a satellite communication system, the terminal comprising: anaperture having radiating antenna elements operable to radiate radiofrequency (RF) signals; a modem coupled to the aperture; a blockupconverter (BUC) coupled to the modem; and a controller coupled to themodem and the BUC and operable to obtain a value representing a maximumallowed Power Spectral Density (PSD) for the scan and skew of theaperture, determine a maximum allowable modem output power based on thevalue representing a maximum allowed PSD and based on a power transfercurve of a BUC power to modem power relationship, the maximum allowablemodem output power being that which ensures that transmissions from theterminal do not exceed the maximum allowed PSD if the maximum allowablemodem output power is not exceeded by the modem, and send an indicationof the maximum allowable modem output power to the modem, wherein theaperture transmits wirelessly based on modem output power in accordancewith the maximum allowable modem output power.
 10. The terminal definedin claim 9 wherein the controller is part of an antenna subsystem module(ASM) that includes the aperture.
 11. The terminal defined in claim 9wherein the maximum allowable modem output power is determined withoutcommunication with a hub in a satellite communication system in whichthe aperture transmits satellite communications.
 12. The terminaldefined in claim 9 wherein the maximum PSD value is that which meets aregulatory limit.
 13. The terminal defined in claim 9 wherein thecontroller determines the maximum allowable modem output power by:determining an Equivalent Isotropic Radiated Power (EIRP); obtaining anantenna gain; determining a maximum BUC power based on the EIRP and theantenna gain; and determining the maximum allowable modem output powerbased on the maximum BUC power.
 14. The terminal defined in claim 13wherein the controller obtains the antenna gain by calculating theantenna gain based on elevation angle.
 15. The terminal defined in claim13 wherein the controller determines the maximum BUC power based on theEIRP and the antenna gain by subtracting the antenna gain from the EIRP.16. One or more non-transitory computer readable media storinginstructions thereon which, when executed by a terminal having anantenna, a modem a block upconverter (BUC) coupled to the modem, and acontroller, cause the terminal to perform a method comprising:determining the scan and skew of the antenna; obtaining, using thecontroller, a value representing a maximum allowed Power SpectralDensity (PSD) for the determined scan and skew; determining, using thecontroller, a maximum allowable modem output power based on the valuerepresenting a maximum allowed PSD and based on a power transfer curveof a BUC power to modem power relationship, the maximum allowable modemoutput power being that which ensures that transmissions from theterminal do not exceed the maximum allowed PSD if the maximum allowablemodem output power is not exceeded by the modem; sending, using thecontroller, an indication of the maximum allowable modem output power tothe modem; and performing one or more transmissions from the terminalbased on modem output power in accordance with the maximum allowablemodem output power.
 17. The one or more non-transitory computer readablemedia defined in claim 16 wherein determining the maximum allowablemodem power comprises: determining an Equivalent Isotropic RadiatedPower (EIRP); obtaining an antenna gain; determining a maximum blockupconverter (BUC) power based on the EIRP and the antenna gain; anddetermining the maximum allowable modem output power based on themaximum BUC power.
 18. The one or more non-transitory computer readablemedia defined in claim 17 wherein obtaining the antenna gain comprisescalculating the antenna gain based on elevation angle, determining themaximum BUC power based on the EIRP and the antenna gain comprisessubtracting the antenna gain from the EIRP, and determining the maximummodem output power is based on a power transfer curve of the BUC powerto modem power relationship.